In the field of floor coverings, resilient products, usually based on PVC, enjoy great success, in a large part due to the variety of decorative possibilities that they permit. Indeed it is possible to print them, to produce chemical or mechanical embossing optionally in connection with printed designs, to produce material effects by combining various types of particles, resulting in graining, imitations of stones or other mineral or more generally natural effects.
Regarding these material appearances which increasingly appeal to the public and to which the invention relates, two techniques coexist.
The first, which results in the formation of the family of products known as “homogeneous products” comprises the following steps:    1 Extruding a certain number of films having different colors or mattness from a thermoplastic material, generally PVC    2 Mechanically granulating these films in order to obtain particles having more or less spherical shapes of the order of 5 mm in diameter (function of the final thickness of the product)    3 Mechanically mixing these particles as a function of the appearance desired for the finished product and distributing them on a conveyor using a Villars® type dispenser. In general, a deposition of a single layer of particles is aimed for, that is to say that particles are all in contact with the conveyor and only overlap very little. Since standard dispensers do not permit a deposition that is that uniform, in order to achieve this objective the conveyor may be subjected to vibrations, as the particles are free, the “overflow” may be discharged via the edges of the conveyor.    4 Introducing this assembly of particles into a Hymmen® type double-belt press. These machines act as a calender but make it possible to keep the particles at the desired softening point of the thermoplastic material for several seconds by gradually compressing it. They therefore avoid deforming the particles too much and creating (directional) line effects in the finished product. During the softening under high pressure (up to 40 bar) the particles based on the same thermoplastic material agglomerate with one another, their peaks are crushed so that the product formed has the appearance of a continuous film with perfectly smooth surfaces.
Each particle, with its color or mattness characteristics, nevertheless remains visible as is, although deformed, which gives the product its specific appearance.
This product is constituted of a single homogeneous layer of materials (homogeneous since being of the same chemical nature), hence its name.
When this material is subjected to traffic as a floor covering, its wear will not give rise to a variation in appearance since the product is, by construction, also homogeneous in its thickness (a single layer of particles deposited on the conveyor).
These products do not therefore intrinsically need additional protection with respect to the traffic linked to their use, that is to say, as for products based on plastisol (see below), a wear layer (or smoothing layer) generally deposited in liquid form at the end of the production process, then gelled in an oven.
These products make up a family that is highly valued for its strength qualities.
The particles may have a wide range of colors or mattness. Different esthetic effects may be obtained by varying the diameter of the particles, or even by mixing particles of different diameters.
Sophisticated embodiments exist which consist in producing relatively coarse designs via a system of covers or drawers arranged below dispensers or in using particles of uncommon sizes or shapes, as is described in patent EP 1838510.
Nevertheless, it remains impossible, with this technique, to combine particles of different chemical natures and even less mineral or metallic particles, nor particles of non-spherical flake type since these particles will inevitably be deformed during the process. The esthetic range linked to this process is therefore greatly limited.
The second, which results in the formation of the family of products known as “heterogeneous” products is based on the use of plastisol (mixture of PVC, plasticizer and optionally filler) which is in a liquid form.
In order to form products known as “heterogeneous” products:    1 Using a doctor blade or rolls or any other suitable means, a first liquid layer of colored plastisol, opaque plastisol or transparent, and therefore unfilled, plastisol (whereas a normal plastisol is 50% filled with, in general, calcium carbonate) is deposited on a substrate which may be, for example, a calendered film reinforced with a web of glass fibers.    2 Particles are then sprinkled over this layer of plastisol using a dispenser, for example of Villars® type.    3 At this stage, the penetration of the particles into the plastisol is not controlled. The particles remain predominantly at the surface, thus creating a random relief.    4 Furthermore, it is impossible to obtain a single-layer type deposition (no vibration possible due to the viscosity of the plastisol) and if it is attempted to remove the excess particles via suction for example, they will inevitably be contaminated by the plastistol which will make them unable to be recycled and will create multiple pollution problems.    5 The product is then pre-gelled. This is to say that it passes under an infrared assembly or into an oven, which will enable a first curing of the plastisol, therefore setting the particles.    6 A new layer of transparent plastisol known as smoothing plastisol is then deposited, the role of which will be to seal the product, that is to say to fill in the voids between the particles or the surface irregularities that the dropping thereof has inevitably caused in the plastisol medium. This plastisol, which is unfilled or not filled very much, is therefore expensive. Furthermore, it is never strictly speaking perfectly transparent and will therefore cause a “milky” haze on top of the decoration produced by the particles.    7 This deposition is followed by a gelling in an oven which will ensure the definitive cohesion of the covering.
These two succinct descriptions therefore clearly make it possible to comprehend the advantages and drawbacks of each of these two families of products.
Homogeneous products do not require a transparent smoothing (or wear) layer but remain limited esthetically due to the restricted type of particles that can be used, (due, in particular, to their deformation), whilst heterogeneous products based on plastisol, although they can use particles of all shapes and natures by blending them with one another, require a large supply of “transparent” plastisol which is therefore expensive since it is lightly filled, which will furthermore blur the reading of the decoration, and also a wear layer based on PU, and therefore also expensive.
With this second technique, appearances close to homogeneous are also impossible to achieve due to the plastisol/dispenser combination which does not allow the deposition of a single layer.
The read quality of the decoration is poorer than in the case of homogeneous products due to the addition of the smoothing plastisol, the particles never strictly speaking being at the surface of the covering.
Finally, the current processes using plastisol require a large number of separate successive steps that it is necessary to control individually and which generally increase the production costs.
To date, these techniques have therefore remained complementary, each being confined to its esthetic and economic range.